In general, in the washing machine, there are a pulsator type washing machine in which a washing tub rotates in a vertical position, and a drum type washing machine in which the washing tub rotates in a horizontal position.
Particularly, the drum washing type, carrying out washing by using a friction of laundry and a drum rotated as a driving power of a motor is received, gives almost no damage to the laundry, causes no entangling of the laundry, and can provide pounding and rubbing effects.
One exemplary related art direct coupling type drum washing machine will be explained, with reference to FIG. 1, briefly. FIG. 1 illustrates a section of one exemplary related art direct coupling type drum washing machine, provided with a tub 3 inside of a cabinet 5, and a drum 9 inside of the tub 3.
There is a drum shaft 13 fitted to the drum 9 for transmission of a driving power of the motor 6 to the drum 9. There are bearings 12 in front and rear of the drum shaft 13, and a bearing housing in a central part of a rear wall of the tub 3. There is a stator 7 of the direct coupling type motor 6 fixed to a rear wall part of the tub 3 and a rotor 8 of the direct coupling type motor 6 on the drum shaft 13 together with the stator 7. According to this, the drum 9 is directly coupled to, and rotated with the rotor 8.
In the meantime, there is a door 1 in front part of the cabinet 5, and there is a gasket 2 between the door 1 and the tub 3. There are hanging springs 4 between an inside of an upper part of the cabinet 5 and an upper side of an outside circumference of the tub 3 for supporting the tub 3, and there is a friction damper 10 between an inside of a lower part of the cabinet 5 and a lower side of an outside circumference of the tub 3, for attenuating vibration of the tub 3 occurred during spinning. There is a motor sensor 11 at one side of the motor 6 for detection of a revolution speed of the rotor 8.
In the meantime, in the foregoing direct coupled drum washing machine, revolution speed control of the drum 9 is carried out during spinning as follows. When the rotor 8 starts to rotate as the spinning starts, the motor sensor 11 keeps to detect a revolution speed of the rotor 8, and transmits to a controller (not shown), and the controller compares if the revolution speed of the rotor 8 is reached to a desired revolution rate.
If the revolution speed of the rotor 8 is reached to a revolution speed (for an example, 110 rpm) the laundry is stuck to, and does not fall off from, an inside wall of the drum 9, an eccentricity of the laundry is detected, and if the eccentricity is determined to be higher than an allowable value, the drum is rotated again after the drum is stopped, and if the eccentricity is determined to be lower than an allowable value, the revolution speed of the rotor 8 is increased gradually.
That is, because rotation of the drum 9 under a state the eccentricity is excessive at an initial spinning affects to a general rigidity of the system, such as breaking the bearing 12 supporting the drum shaft 13 or breaking the tub 3, a full scale spinning is progressed after the eccentricity is controlled under a preset value.
On the other hand, if the eccentricity is determined to be below the allowable value, the revolution speed of the rotor 8 is increased step by step until the revolution speed reached to a maximum spinning speed, when the revolution speed of the rotor 8 is increased no more, but is maintained.
In the increase of the revolution speed of the rotor 8 to the maximum revolution speed for progressing spinning, the revolution speed of the rotor 8 is controlled by means of a duty value and a lead angle.
At first, the duty value is increased by PWM (Pulse Width Modulation) to a revolution speed (for an example, 1000 rpm) below the maximum revolution speed (for an example, 1400 rpm), and remained portion of the revolution speed required to reach to the maximum revolution speed is increased by controlling the lead angle for bringing the revolution speed into line with a desired maximum revolution rate.
The control of the motor 6 speed by controlling the duty value and the lead angle is made as follows.
At first, the duty value, varied by PWM control, is a value varied up to 0–250, and the revolution speed of the rotor 8 is varied with the value, such that the greater the duty value, the higher the revolution of the rotor. The lead angle controls a spinning speed by controlling a phase difference of a current and a voltage, of which purpose lies on bringing waveforms of the voltage and the current into conformity by making the voltage applied earlier than the current within 0–75° phase taking a fact that the phase of the current is later than the voltage into account, and it is favorable that the waveforms of the voltage and the current are in conformity in view of power consumption.
However, the related art direct coupling type drum washing machine has the following problems in the method for controlling the spinning speed.
That is, though the process proceeds to a high speed spinning as the eccentricity is detected to be below a present value at an initial detection of the eccentricity, if an eccentricity greater than a preset value is actually occurred due to change of the eccentricity during the spinning, or inaccurate detection of the initial eccentricity, the spinning is progressed as the lead angle increases gradually until the present maximum revolution speed is reached.
Once this happens, because it is dangerous as an excessive force is applied to an entire system, such as a heavy load being applied to the motor 6, it is designed that a maximum value of the lead angle is controlled to be below a preset value (for an example; 65°).
However, in the related art, not only the maximum lead angle value is fixed as one value, but also the lead angle value is set to a value greater by a certain extent than an actual lead angle required for reaching to the maximum spinning speed when the rated voltage and eccentricity are normal.
When the lead angles are the same, the spinning revolution speed is varied with the applied voltage, such that the higher the applied voltage, the higher the spinning revolution rate.
Accordingly, in the related art as shown in FIG. 4, when a voltage higher than the rated voltage is applied under a state when both the lead angle and the load are the same, the allowable eccentricity for reaching to the maximum speed of the drum 9 becomes also greater because the revolution speed of the rotor 8 and the drum 9 directly coupled thereto become the higher compared to a case the rated voltage is applied.
However, if the eccentricity is greater than a certain amount (for an example, 300 g) under a state the drum 9 is reached to the maximum revolution speed, an excessive load is applied to the entire washing machine system due to the excessive eccentricity over the regular allowable value, which at the end weakens a rigidity as an overstrain is given to the entire system, such as motor, and the like.
In the meantime, in the related art as shown in FIG. 4, there has been a disadvantage that the maximum spinning speed can not be reached even if the lead angle is increased up to a maximum lead angle despite of a small eccentricity though the applied voltage is low.